If you use OS X, then you own an application that’ll waste hours of your time. And it’s just sitting on your hard drive.
Say hello to
Applications > Utilities > Grapher.
We needed a simple Fourier square wave for a book. Just type in the equations, and out it pops.
But the time wasting comes from playing with its example graphs.
Did I mention that they animate, and it can export Quicktime?